This invention relates to selectively magnetizing nonmagnetic or paramagnetic particles and to magnetizing reagents useful for that purpose.
Magnetic separation can be an inexpensive, selective and efficient method for separating a particulate mixture. Many techniques have been used to magnetize nonmagnetic or paramagnetic particles to permit them to be selectively separated from a mixture by magnetic separation.
For example, U.S. Pat. No. 3,926,789 to Shubert discloses wetting the surface of mineral particles with an emulsified magnetic fluid to render them magnetic. C. de Latour, Journal of American Waterworks Association, Vol. 68, p. 443 (1976) discloses using an inorganic coagulant, such as ferric chloride or aluminum sulfate, to agglomerate particles nonselectively in a system which contains a mixture of magnetite and other materials. J. Y. Hwang, et al., IEEE Transactions on Magnetics, Vol. MAG-18, No. 6, p. 1689 (1982) discloses adding an organic polymer flocculant to a mixture of magnetite and other minerals to yield a selective co-flocculation of magnetite and desired minerals.
U.S. Pat. Nos. 4,285,819 to Yen, et al. and U.S. Pat. No. 4,554,088 to Whitehead, et al. disclose methods which involve coating magnetic materials with a polymer and then coupling the polymer-coated magnetite particles to the particles to be magnetized. P. Parsonage P, IMM Tenth Annual Commodity, Paper No. W86007 (1985) discloses introducing fine magnetite into a pulp of mineral slurries in which the desired minerals are conditioned to carry a surface charge opposite to that of magnetite to favor coating of magnetite.
U.S. Pat. Nos. 4,019,995, to Briggs, et al 4,094,804, to Shimoiizaka, 4,208,294, to Khalafalla, et al, 4,356,098 to Chagnon and 4,430,239 to Wyman disclose ferrofluids which are Newtonian liquids containing suspended, small magnetic particles which do not settle out under the influence of gravity and an external magnetic field.